This proposal is concerned with thermodynamics, perturbation kinetics, and conformational studies of the interactions on the molecular level of tubulin with anti-cancer drugs which act by interfering with microtubule formation. The mechanism of binding to tubulin of vinblastine, vincristine and related compounds, as well as of colchicine, and the induced self-associations of tubulin will be investigated in detail, with particular emphasis on the linkage between binding, self-association, and interactions with other ligands, using sedimentation velocity, perturbation kinetics and binding techniques, with computer simulation where necessary. Distances between identified independent sites of liganding will be measured by fluorescence energy transfer on tubulin molecules in various conformational states, -unpolymerized, microtubules, liganded to colchicine and vinblastine. Rigorous analysis in terms of quantitative thermodynamic, kinetic and conformational concepts will be applied to the results, with the anticipation that a detailed quantitative understanding of the mechanism of action of these anti-cancer drugs on the molecular level will help in the rational design of more effective chemotherapeutic agents.